This letter was originally published in our 2024 Annual Report.
The past year at ISRG has been a great one and I couldn’t be more proud of our staff, community, funders, and other partners that made it happen. Let’s Encrypt continues to thrive, serving more websites around the world than ever before with excellent security and stability. Our understanding of what it will take to make more privacy-preserving metrics more mainstream via our Divvi Up project is evolving in important ways.
A certificate fundamentally only does the following, it binds a name and a public key together and attaches a signature to that binding.
Anyone can make a certificate binding any key to any name and put their own signature on it, they just can’t fake others people’s signatures. This is also what you do if you self sign a certificate. If you then install the public key of your signing key in your webbrowser you can connect to your own services using your TLS key and your browser will check that the server presents the certificate with a matchign signature proving that it is using the right TLS key.
You can also bind your TLS key to www.wikipedia.org and sign it. However nobody else knows your signing key, and thus nobody would trust the certificate you signed. Which is a good thing, because otherwise it would be easy for you to impersonate Wikipedia’s website.
The value of trusted certificates lies in the established trust between the signers (CAs) and the software developers who make browsers etc. The signers will only sign certificates to bind names and TLS keys for the people who actually own the name, and not for third parties.
The validation of ownership is the thing that varies a lot. The simple way is just checking for control of the web server currently reachable under a name, or checking for control of the DNS entries for a name, but the more complicated validations check business records etc.
So when you’re asking do they protect better, it’s kind of difficult to say.
If you can validate the signature yourself, say you have control of the browser and the server, then your own signature is fine, and a trusted one wouldn’t be any better.
But if you want third parties, that don’t know you, to be able to verify that their TLS session is established to a person who actually owns the domain, rather than a man in the middle, then the only practical solution today is using that established trust system.
If you are asking about the encryption strength of the TLS session itself, then that’s completely independent of the certificate issue, because again the certificate only binds a name to a key with a signature. You can bind an old short key, whose private key has been leaked before to a name, or you can bind a modern long key that is freshly generated to the same name. You can used either key in a good or a bad cryptographic setup. You can use deprecated SSL 3.0 or modern TLS 1.3. Those choices don’t depend on who signs the certificate.
Not at all, thank you for actually trying to answer my question instead of just telling me how it is supposed to work!
Just quickly, no I didn’t wonder about the keys encryption strength, what I do wonder about is if it is overall more secure to use a “trusted” entity, than, if the browsers weren’t locked down, my own home-generated signature.
I mean, if someone tries to “man in the middle”, or maskerade as my website, the trusted stuff will not add any security.
If someone hacks my site, and then maskerades as me (or does their shenanigans) the trusted stuff doesn’t add any security there either. They can just use my installed all set up “Trusted tm” certificate until it expires (my home made cert will expire too BTW).
So, for now, I don’t see any benefit to this except the trusted entity gets to have control over it all (and earn some money).
I bet there are smarter people than me out there who knows why I’m wrong, hence all the noobie questions.
I mean, if someone tries to “man in the middle”, or maskerade as my website, the trusted stuff will not add any security.
As long as they can obtain a certificate signed by a trusted signer for your name, you are correct. And you are touching on a real issue here. The number of trusted signers in the browser stores is large, and if only one can be tricked or compromised, then the MitM can generate a certificate your browser would trust just as well as your own original one.
If someone hacks my site […]
then it’s over anyway, yes. The signature on the certificate only validates your TLS key as being one that was properly assigned to the holder of your domain name. Once the endpoint is compromised, TLS doesn’t matter anymore.
if the browsers weren’t locked down
Actually maybe they aren’t as locked down as you think. To my knowledge you can add your own signing key certificates to your local installation of Firefox, Chrome and the Windows cert storage. In fact there are companies who do this a lot. They Man-in-the-Middle all their employees, with a proxy that does security scanning. For this reason they will deploy their signing keys internally. So the browsers still work. You can use these mechanisms for yourself if you like.
A certificate fundamentally only does the following, it binds a name and a public key together and attaches a signature to that binding.
Anyone can make a certificate binding any key to any name and put their own signature on it, they just can’t fake others people’s signatures. This is also what you do if you self sign a certificate. If you then install the public key of your signing key in your webbrowser you can connect to your own services using your TLS key and your browser will check that the server presents the certificate with a matchign signature proving that it is using the right TLS key.
You can also bind your TLS key to www.wikipedia.org and sign it. However nobody else knows your signing key, and thus nobody would trust the certificate you signed. Which is a good thing, because otherwise it would be easy for you to impersonate Wikipedia’s website.
The value of trusted certificates lies in the established trust between the signers (CAs) and the software developers who make browsers etc. The signers will only sign certificates to bind names and TLS keys for the people who actually own the name, and not for third parties.
The validation of ownership is the thing that varies a lot. The simple way is just checking for control of the web server currently reachable under a name, or checking for control of the DNS entries for a name, but the more complicated validations check business records etc.
So when you’re asking do they protect better, it’s kind of difficult to say.
I hope that helps, sorry for writing so much
Not at all, thank you for actually trying to answer my question instead of just telling me how it is supposed to work!
Just quickly, no I didn’t wonder about the keys encryption strength, what I do wonder about is if it is overall more secure to use a “trusted” entity, than, if the browsers weren’t locked down, my own home-generated signature.
I mean, if someone tries to “man in the middle”, or maskerade as my website, the trusted stuff will not add any security.
If someone hacks my site, and then maskerades as me (or does their shenanigans) the trusted stuff doesn’t add any security there either. They can just use my installed all set up “Trusted tm” certificate until it expires (my home made cert will expire too BTW).
So, for now, I don’t see any benefit to this except the trusted entity gets to have control over it all (and earn some money).
I bet there are smarter people than me out there who knows why I’m wrong, hence all the noobie questions.
Cheers!
As long as they can obtain a certificate signed by a trusted signer for your name, you are correct. And you are touching on a real issue here. The number of trusted signers in the browser stores is large, and if only one can be tricked or compromised, then the MitM can generate a certificate your browser would trust just as well as your own original one.
then it’s over anyway, yes. The signature on the certificate only validates your TLS key as being one that was properly assigned to the holder of your domain name. Once the endpoint is compromised, TLS doesn’t matter anymore.
Actually maybe they aren’t as locked down as you think. To my knowledge you can add your own signing key certificates to your local installation of Firefox, Chrome and the Windows cert storage. In fact there are companies who do this a lot. They Man-in-the-Middle all their employees, with a proxy that does security scanning. For this reason they will deploy their signing keys internally. So the browsers still work. You can use these mechanisms for yourself if you like.
Example documentation: https://support.mozilla.org/en-US/kb/setting-certificate-authorities-firefox